Field of the Invention
The present invention relates to an endoscope illuminating optical system.
Description of the Related Art
It is preferable that an endoscope intended for urinary organs, which is to be inserted transurethrally, is insertable into a urethra, and has an outer diameter not larger than 7 mm. In such manner, the endoscope for urinary organs has a diameter thinner than a diameter of an endoscope for alimentary track which is widely known for a medical examination of stomach or large intestine. Moreover, since the urinary organs are generally filled with urine, an optical design envisaged for in-water observation is necessary.
As a technology for in-water wide angle observation with an endoscope, an arrangement proposed in International Unexamined Patent Application Publication No. 2015/015996 for example, is available. In International Unexamined Patent Application Publication No. 2015/015996, it is signified that the medium of observation space in a case of observing the urinary organs with endoscope is a perfusion solution or urine of which water is the main constituent, and that it is reasonable to deem a refractive index of these media to be equivalent to the refractive index of water.
Furthermore, in International Unexamined Patent Application Publication No. 2015/015996, narrowing of an in-water angle of view with respect to an angle of view at the time of in-air observation has been cited. It has been signified that when the refractive index of water for a d-line is let to be 1.333, and an outer surface side of an endoscope objective optical system is let to be a flat surface, a relationship of the in-air angle of view and the in-water angle of view is shown as follows.
In-air angle of view 180° 160° 140° 120°In-water angle of view97.2°95.3°89.7°81.0°
At the time of practical use of an endoscope for urinary bladder with the in-air angle of view of 120°, the in-water angle of view is narrowed to 81°. When an example of the endoscope for urinary bladder is cited, for exploring a pathological lesion inside the entire urinary bladder, an operator carries out a combined operation of bending a front end of the endoscope, inserting and removing an insertion portion, and twisting the insertion portion. When the in-water angle of view is narrow, a frequency of these operations is to be increased, and it becomes difficult to explore the pathological lesion inside the entire urinary bladder efficiently.
In such manner, in the endoscope that carries out the in-water observation, widening of the in-water angle of view has been desired. Securing a light-distribution of an illuminating optical system corresponding to the widened in-water angle of view becomes a challenging task when the in-water angle of view is to be widened. Moreover, in the endoscope for urinary bladder, a thin outer diameter, that can be inserted via the urethra, and mounting of a channel for treatment become indispensable. Consequently, an ability to mount in a narrow front-end space of endoscope is indispensable. Conventional endoscope illuminating optical systems, as an arrangement from a shape point of view, for securing the light-distribution, and mounting in particular, patent literatures from International Unexamined Patent Application Publication No. 2015/015996, International Unexamined Patent Application Publication No. 2010/113550, Japanese Patent Application Laid-open Publication No. 2008-237790, Japanese Utility Model Application Publication No. Sho 62-143918, Japanese Patent No. 4741032 Publication, Japanese Patent Application Laid-open Publication No. Sho 63-239415 have been known.